Krell KSA 50 PCB

Just a comment or two.

The lack of V-I limiter is what makes Krell a Krell. As is, the 'clone' would not be able to do what Krells become famous for - drive insane loads (Apogee Scintilla and like) without compression.

I've never seen an output coil in any of the Krell amps - I doubt it is needed.

All Krell amps from that vintage I've seen had input low pass at around 350kHz or so, hence C101 should be calculated as such.

Despite ridicule from some, KSA50 will whip the pants off most of todays amps with ease, and sound MUCH bigger than its 50W rating suggests.
 
  • Like
Reactions: 1 user
Pavel:
Thanks for correcting me ;)
I must learn not to read and write when I'm tired :(

Bratislav (and others):
The V-I limiter was put in as an additional options for those who would like some kind of protection.
Don't like it ??? Don't use it ;)

The output coil are shown in the schematic for those who will build this amp with new high freq. transistors....
I'm not sure how it will respond to modern components, so better be safe than sorry ;)
And again: Don't like it ??? Don't use it ;)

Please keep the comments comming:D
 
Re: Transformer Specs

Elso Kwak said:


Hi Bratislav,
I was quite serious........

:cool: :cool: :cool:

The quality of transformers in Krell amps I've seen (heard) varied quite a bit. Some were dead quiet, some had quite a buzz.
All were generously specified (more than enough VA to run at rated power even at low impedances). As far as regulation and flux density I woudln't have a clue, I only had one specimen to look up closely(ish), and at 3KW it was reasonably good as far as sagging (<2% I think), but then most big trafos are.
I don't think they were special devices, despite impressive logos on them :)
 
... what makes Krell a Krell.

Physical limits or specification of devices are the same for every manufacturers. In this type of amp, which have probably +/- 50 V rails, two output devices with 15 A colector current each and standard SOAR you cannot " go " with load impedance too low, I mean only to cca 2 Ohms. Apogee boxes, which have impedance ( as I know ) around 1 - 2 Ohms, are for this type of amp dangerous, independent on claims of amp's manufacturer.
 
Re: ... what makes Krell a Krell.

Upupa Epops said:
Physical limits or specification of devices are the same for every manufacturers. In this type of amp, which have probably +/- 50 V rails, two output devices with 15 A colector current each and standard SOAR you cannot " go " with load impedance too low, I mean only to cca 2 Ohms. Apogee boxes, which have impedance ( as I know ) around 1 - 2 Ohms, are for this type of amp dangerous, independent on claims of amp's manufacturer.

Well, even going by theory, 400W peak only requires 20A (10A per device). Pushing it into dangerous waters, definitely, with 20A devices, but real life music only requires these kind of peaks less than 10% of the time. At those power levels the speakers, rooms and owner's eardrums will be giving up probably lot quicker than output transistors.

But more importantly these are not claims, Krells actually WORKED with Apogees - that is how legend was born.

Besides, other Krells used lot more ouput devices than two pairs.
My version of KSA100 for example has 16 20A devices per channel. I don't really think I'd need any V-I limiters even with 1 ohm loads !

(my version == the version I've made as DIY, of course!)
 

Attachments

  • krell.jpg
    krell.jpg
    98.4 KB · Views: 10,156
ACD said:
Any "last minute" changes before I start making the PCB layout ??? ;)
Which size do you prefer ???
Single or double side ???
Other mods ????
;)

Make some room for a switch for a quick change of bias ("winter" and "summer" setting). Every summer when Melbourne temepratures hit 40+ C I wind the bias down and that is a lengthy (and risky) job.